Full request is in a nested field

Also add `model` to the general `GenerateContentRequest`. It is required
when using that pattern for counting tokens.

pkgs/google_generative_ai/lib/src/model.dart

@@ -245,15 +245,15 @@ final class GenerativeModel {
     List<Tool>? tools,
     ToolConfig? toolConfig,
   }) async {
-    final response = await _client.makeRequest(
-        _taskUri(Task.countTokens),
-        _generateContentRequest(
-          contents,
-          safetySettings: safetySettings,
-          generationConfig: generationConfig,
-          tools: tools,
-          toolConfig: toolConfig,
-        ));
+    final response = await _client.makeRequest(_taskUri(Task.countTokens), {
+      'generateContentRequest': _generateContentRequest(
+        contents,
+        safetySettings: safetySettings,
+        generationConfig: generationConfig,
+        tools: tools,
+        toolConfig: toolConfig,
+      )
+    });
     return parseCountTokensResponse(response);
   }
 
@@ -319,6 +319,7 @@ final class GenerativeModel {
     tools ??= _tools;
     toolConfig ??= _toolConfig;
     return {
+      'model': '${_model.prefix}/${_model.name}',
       'contents': contents.map((c) => c.toJson()).toList(),
       if (safetySettings.isNotEmpty)
         'safetySettings': safetySettings.map((s) => s.toJson()).toList(),

samples/dart/bin/simple_text.dart

@@ -22,7 +22,13 @@ void main() async {
     stderr.writeln(r'No $GOOGLE_API_KEY environment variable');
     exit(1);
   }
-  final model = GenerativeModel(model: 'gemini-pro', apiKey: apiKey);
+  final model = GenerativeModel(
+      model: 'gemini-pro',
+      apiKey: apiKey,
+      safetySettings: [
+        SafetySetting(HarmCategory.dangerousContent, HarmBlockThreshold.high)
+      ],
+      generationConfig: GenerationConfig(maxOutputTokens: 200));
   final prompt = 'Write a story about a magic backpack.';
   print('Prompt: $prompt');
   final content = [Content.text(prompt)];